Treatment of limestone formations



Uni d smsl fi c TREATMENT OF LHVIESTONE FORMATIONS William E. Thompson, Wallingford, and Francis A. Boyle,

Norwood, Pa., assignors to Sun Oil Company, Philadelphia, Pa., a corporation of New Jersey No Drawing. Application May 2, 1956 Serial N0. 582,074

'3 Claims. (Cl. 2528.'55)

This invention relates to the treatment of limestone formations which contain petroleum hydrocarbons for the purpose of facilitating the flow of such hydrocarbons from the formation into a production well. More particularly, the invention involves the use of certain organic amines for treating calcareous formations to improve the flow of hydrocarbons therethrough while hindering the flow of water.

It has been proposed heretofore to treat oil sands with various organic amines to facilitate the production of petroleum from the formation. Such treatment is beneficial due to the fact that the amines tend to become chemi-sorbed on the surface of the sand grains and thereby render the sand preferentially wettable by oil rather than by water. This permits oil to flow through the pores more readily while hindering the flow of water into the zone which has been treate The usefulness of amines as treating agents, however, heretofore has been considered as limited to the treatment of formations which are siliceous in nature. The effectiveness of this type of compound in improving the flow of oil has been attributed to the acidic character of the sand, which is thought to result from the ionization of surface molecules of silicic acid. The basic-reacting amines thus have been thought to be retained on the sand by chemi-sorption essentially as a result of its acidic properties. Accordingly, it has been considered heretofore that amines would have no usefulness whatever in treating limestone formations, since limestone is essentially basic rather than acidic and therefore would not be expected to react with an amine.

It has now been surprisingly discovered that certain aliphatic amines are outstandingly effective for treating limestone formations. According to the invention, a limestone formation is treated with a hydrocarbon solution containing, as the active treating agent, a minor amount of an aliphatic amine having 8-12 carbon atoms. We have found that such treatment will substantially increase the permeability of the limestone to hydrocarbons while decreasing its permeability to water. The invention thus provides a simple and effective treatment for facilitating the flow of oil while hindering the flow of water through an oil-bearing limestone formation.

The amines which are useful in practicing this invention are octylamine, nonylamine, decylamine, undecylamine, dodecylamine and their isomers. Individual amines of this group can be employed in treating limestone formations or mixtures of such compounds can be used with good results. The'preferred compound for practicing the invention is decylamine which has been found to be especially elfective in increasing the permeability of limestone to hydrocarbons while decreasing its permeability to water.

The treatment of a petroleum-bearing limestone formation according to the invention may be carried out by Wise maintaining comparable treating conditions.

2,908,643 Patented Oct.- 13, 1959 dissolving a minor amount of the amine in a suitable hydrocarbon solvent, such a kerosene, gas oil, crude oil or the like, and introducing the solution through a borehole into the formation. Only a small proportion, e.g. less than 5%, of the amine need be used in the solution for good results, although larger proportions may be employed if desired. Generally it is preferable that the amount of amine in the treating agent solution be within the range of ODS-2.0% by weight, since it has been found that such small proportions can effectively and economically be employed to achieve the desired results. As the solution of treating agent flows from the borehole into the formation being treated, it tends to reduce the water content of the formation in the vicinity of the borehole by displacement of the water phase farther back into the formation and thus open the channels for hydrocarbon flow. It also appears to change the character of the limestone surfaces in some beneficial manner, perhaps by rendering them preferentially oil wettable. When the well is subsequently put back into operation, the formation hydrocarbons can pass more readily through the treated Zone whereas the flow of water from farther back in the formation toward the borehole is retarded. The treatment thus effects an increase in the ratio of oil to water produced from the well.

For the purpose of illustrating the effectiveness of the invention, two comparative runs were made with limestone cores, using difierent treating agents but other- One of the treating agents was a mixture of amines composed mainly of decylamine with small amounts of octylamine and dodecylamine. The treating agent for the comparative run was caprylic acid, this being selected because of its acidic character which normally could be expected to cause chemi-sorption thus rendering the limestone preferentially oil wettable.

, In each of the runs the procedure comprised treating a cylindrical limestone core of about LD. and 2 /2 length is a specially designed flow cell first with brine and then with kerosene under selected conditions until equilibrium flow rates had been reached. The core was then treated by flowing therethrough a kerosene solution containing 0.10% of the treating agent until equilibrium flow again was reached The amount of residual brine removed from the core by such treatment and its change in permeability to kerosene Were determined.

In the run carried out according to the invention employing the aforesaid mixture of amines, the permeability of the limestone core to kerosene was 0.1 millidarcy prior to introducing the treating agent and it increased to 8.5 millidarcies during the treatment. Also,

, the treatment removed an amount of residual brine from the core equal to 37% of the pore volume. Following this treatment kerosene alone was passed through the core, and it was found that the permeability increased still further to 10 millidarcies. By way of comparison the treatment carried out utilizing caprylic acid raised the permeability from only 0.20 to 0.32 millidarcy and no residual brine was removed from the core.

The foregoing comparative results illustrate the sur-' References Cited in the file of this patent UNITED STATES PATENTS Blair Oct. 12, 1943 Albaugh Apr. 29, 1947 

1. METHOD OF FACILITATING THE FLOW OF HYDROCARBONS FROM A LIMESTONE FORMATIOM INTO A BOREHOLE WHICH COMPRISES TREATING SUCH LIMESTONE FORMATION WITH A HYDROCARBON SOLUTION CONTAINING 0.05-5% BY WEIGHT OF AN ALIPHATIC AMINE HAVING 8-12 CARBON ATOMS. 